I'm an Android (Droid on 2.1) guy these days but, for the most part, apps available to iPhones are available for us too (except they're cheaper/free for us).
Anyway, what are your favorites?
Mine (all free):
HIIT Interval Timer - Like the Gym Boss, only free.
Calorie Counter - Best all-around app. It has nutritional info for just about any item with a barcode on it (has a barcode scanner too), info on restaurant food, info custom food items by ingredients, diet...